Let us describe the invention using a magnetic disk device as a disk device in question. In order to raise the recording density of a disk, flying height of a head has been reduced year after year and has reached a level of 10 nm or less. In the meantime, the track pitch is also shrinking and has reached a level of 1 μm or less. These trends are causing the following problems:
(1) If physical contact occurs between the head and the disk during a disk operation due to a certain problem, it is necessary to detect the contact and alert the host computer to cause the head to move out of the data area.
(2) In the case of a dynamic loading type magnetic disk device in which the head is moved out of the disk when the disk is not in operation, it is necessary to check if any disturbance exists in the disk device prior to the loading of the head on the disk and to interrupt the loading if any disturbance is found.
(3) As the flying height diminishes to 10 nm or less, it becomes difficult to confirm if the head is truly floating at a designed height on an actual disk device when it is assembled.
(4) Since a disk tester currently available on the market uses a slider that differs in shape from the actual head for a gliding height test for testing the heights of disk surface protrusions, accuracy of measurement is poor. Moreover, since the gliding height test and a confirmation test for checking recording and reproduction characteristics of the disk are carried out on separate heads, a longer testing time is required.
(5) As the track pitch becomes narrower, a servo band needs be increased when the head is following the tracks, which in turn may cause problems such as torsional resonance of a head suspension.
The following proposals have been made for these problems.
As a countermeasure to deal with the contact problem between the head and the disk as described above under (1), U.S. Pat. No. 5,856,895 proposes a method for providing a piezoelectric element on the side of a head slider so that the piezoelectric element oscillates to generate a voltage when a contact occurs between the head and the disk during the disk operation. The method intends to detect the contact between the head and the disk by means of such signal, but a typical slider currently used most widely is so small as 1.2 mm in length, 1 mm in width, and 0.3 mm in height. Therefore, it is difficult to secure a space for mounting a piezoelectric element. U.S. Pat. No. 5,777,815 discloses a method for using a thermal asperity output of a magnetic resistance effect head (“MR head”), however it is only a MR head portion that detects an impact, which is no more than 1 μm in width. Thus, the area of the portion that can be used as a sensor is very small, and moreover, a contact cannot be detected if the contact occurs between the disk and other portions than the MR device on the slider.
As for the problem of (2), Toshiba Technology Disclosure Vol. 17-55, File No. 99169634 disclosed a method for detecting disturbances by adding an acceleration sensor, but the method leads to a cost increase as it requires an additional sensor.
As for the problem of (3), although there is a possibility of measuring the flying height of an assembled actual device by using the thermal asperity output of the magnetic resistance effect head (“MR head”) as described in the aforementioned U.S. Pat. No. 5,777,815, a problem exists in that it cannot detect a contact if the contact occurs between the disk and other portions than the MR device, in like manner as in (1).
As for the problem of (4), JP-A-9-259401 discloses a method for using the magnetic distortion effect of an electromagnetic induction type magnetic head but a problem exists in that the detection sensitivity is too low. Also, JP-A-10-27342 discloses a method for measuring a gliding height using the thermal asperity output of the magnetic resistance effect head (MR head), but a problem exists in that it takes more than 10 minutes to check one disk because the width of the MR device is so small as 1 μm.
As for the problem of (5), U.S. Pat. No. 6,005,750 discloses an idea of damping the torsional resonance of the suspension by adding a damper to a load beam of the head suspension. However, the suspension is getting even smaller and shorter these years so that it is difficult to attach a damper due to such space restriction.